Low-Power Data Loop Recorder

ABSTRACT

A system and method are disclosed for capturing pre- and post-event data for random events using minimum power. Real-time data is captured and stored in a continuous loop in a segment of a first memory. Upon detection of a designated event, a second memory is powered-on and post-event data is stored to a segment of the second memory. After a designated data capture window, the second memory is powered-off and real-time data is captured in an unused segment of the first memory. The post-event data may be captured in the unused segment of the first memory and later transferred to the second memory. Auto-address logic monitors and controls the storage and retrieval of pre- and post-event in the first and second memory. An energy management system determines and controls which segments of the first and second memory should be powered-on or kept in the stasis mode to store event data.

TECHNICAL FIELD

Embodiments of the invention are directed, in general, to data looprecorder memories and, more specifically, to reducing power consumptionin data loop recorders that capture both pre-event and post-event data.

BACKGROUND

Power consumption and battery life are major concerns in remote orinaccessible data loop recorders, such as deployed field equipment ormedical sensors. Data loop recorders typically sample data whentriggered by a specific event. The data is stored for later reading,downloading or transmission. Often, it is desirable to capture data thatprecedes the triggering event (i.e. pre-event data) as well aspost-event data. Because the exact time that a triggering event willoccur is unknown, the data loop recorder memory must be powered-on atall times in order to capture pre-event data. This requires higher powerconsumption than desired in devices that are already power limited bybattery capacity. As a result, the available memory, functionality, andlongevity in battery-powered data loop recorders are limited.

SUMMARY

Embodiments of the invention partition the loop recorder memory in aunique manner and dynamically control the memory power to lower powerconsumption. Embodiments of the invention include the use of four majorfunctional blocks: Inner Loop Memory, Outer Loop Event Memory, EnergyManagement System, and Auto-Address Logic as described below.

Inner Loop Memory (ILM) is a segmented memory that operates in analways-on power state. ILM captures pre-event data in a continuous loop.In one embodiment, a new ILM memory segment is used for each new event.Outer Loop Event Memory (OLM) is maintained in an ultra-low-powerretention mode or stasis mode until an event is detected. Upon receivingan event trigger, post-event data is stored into the OLM in oneembodiment. After the post-event data is captured, the OLM reverts backinto the stasis mode. In alternative embodiments, the OLM memory may besegmented and the power for each segment may be dynamically controlledby the Energy Management System (EMS). The EMS determines and controlswhich segments of the OLM should be powered-on or kept in the stasismode. An Auto-Address Logic (AAL) block maintains address mappingbetween the ILM and OLM. The AAL also manages event trigger generationby processing raw data (e.g. pre-event data) to identify significantevents that should be recorded. The AAL seamlessly provides pre andpost-event data from the ILM and OLM to external devices withoutrequiring additional address manipulation, thereby making the looprecorder device backward compatible with existing applications.

The ILM and OLM may use standard as well custom memories, such as SRAM,Flash, and FRAM. Embodiments of the invention allow for the largest partof the memory—the OLM—to be kept in an ultra-low-power, stasis mode. Thedata loop recorder disclosed herein provides power advantages thatincrease device longevity and allows for the use of more memory (and,therefore, the collection of more data) without increasing the requiredpower level. Embodiments of the invention can be applied to anyrecording application where power saving is critical.

According to one embodiment, a recording device comprises a first memorypartitioned into a plurality of first segments, and a second memorypartitioned into a plurality of second segments. An address logiccircuit is coupled to both the first memory and the second memory. Theaddress logic circuit controls read and write locations for data storedto the first memory and the second memory. An energy management systemis coupled to the second memory. The energy management system controls apower state of the second memory. The energy management system may alsobe coupled to the first memory to control a power state of the firstmemory segments. A data bus is coupled to the first memory and thesecond memory. Real-time data received on the data bus is stored to aselected first memory segment, wherein the selected segment acts as acircular buffer.

A processor is coupled to the address logic circuit, the energymanagement system, and the data bus. The processor monitors datareceived on the data bus and identifies designated events. The processorsends an event trigger to the address logic circuit and to the energymanagement system upon detection of a designated event. The addresslogic circuit may include a pointer table identifying locations ofstored data for a plurality of events. The energy management systemsupplies power to the second memory upon detection of an event trigger,and the address logic circuit causes data to be stored to the secondmemory.

In another embodiment, a method for storing data comprises storing firstpre-event data to a first segment of a first memory. The first segmentoperates as a circular buffer to store a selected duration of recentdata. A first event trigger is received, and first post-event data isstored beginning at a second segment of the first memory during a firstdata-capture period. The first post-event data comprising data receivedafter the first event trigger. The second memory is powered-on, and thefirst pre-event data and first post-event data are transferred to afirst segment of the second memory. The second memory may be powered-onat the end of the first data-capture period. The first pre-event dataand first post-event data may be transferred to the first segment of thesecond memory at the end of the first data-capture period. When thesecond memory is powered-on, either all of segments of the second memoryor only selected segments of the second memory are powered-on. A pointeris stored to identify the location in the first memory corresponding toreceipt of the first event trigger.

A second event trigger may be received during the first data-captureperiod. Second post-event data is stored to the first memory during asecond data-capture period. The second data-capture period may overlapthe first data-capture period. The second pre-event data may overlap thedata stored for the first event. The second pre-event data and secondpost-event data are transferred to a second segment of the secondmemory. A pointer is stored to identify to a location in the firstmemory corresponding to receipt of the second event trigger.

In a further embodiment, a method for storing data comprises storingpre-event data to a first segment of a first memory. The first segmentoperates as a circular buffer to store a selected duration of data. Uponreceipt of an event trigger, a second memory is powered-on. Post-eventdata received after the event trigger is stored to a first segment ofthe second memory during a data-capture period. At the end of thedata-capture period, the second memory is powered-off. The pre-eventdata is transferred to the first segment of the second memory. Thepre-event data and post-event data are combined in chronological orderin the first segment of the second memory. A pointer is stored toidentify a location in the first memory corresponding to receipt of theevent trigger. Second pre-event data is stored to a second segment ofthe first memory. The second segment operates as a circular buffer tostore the selected duration of data. Upon receiving a second eventtrigger, the second memory is powered-on and second post-event data isstored to a second segment of the second memory during a seconddata-capture period. At the end of the second data-capture period, thesecond memory is powered-off. A pointer to a location in the firstmemory corresponding to receipt of the second event trigger.

Alternative embodiments are directed to a recording device comprising afirst memory partitioned into a plurality of first segments. The sizesof the first segments are selected to provide storage for apredetermined pre-event time period. The first memory is optimizedrelative to a second memory to require low access power. The secondmemory is partitioned into a plurality of second segments. The sizes ofthe second segments are selected to provide storage for a predeterminedevent period. The event period comprises both the pre-event period and apost-event period. The second memory is optimized relative to the firstmemory to require low static power. An address logic circuit is coupledto the first memory and to the second memory. The address logic circuitcontrols read and write locations for data stored to the first andsecond memory. An energy management system is coupled to the secondmemory. The energy management system controls a power state of thesecond memory. The energy management system may also be coupled to thefirst memory to control the power state of segments of the first memory.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, wherein:

FIG. 1 illustrates a typical loop recorder data-capture sequence overmultiple trigger events;

FIG. 2 is a block diagram of a data loop recorder according to oneembodiment of the invention;

FIG. 3 illustrates a loop recorder data-capture sequence according toone embodiment of the invention;

FIG. 4 is a block diagram illustrating the capture and storage of datafor multiple events according to one embodiment;

FIG. 5 is a block diagram illustrating the capture and storage of datafor multiple events according to another embodiment; and

FIG. 6 is a block diagram of a monitoring device comprising oneembodiment of the data loop recorder disclosed herein.

DETAILED DESCRIPTION

The invention now will be described more fully hereinafter withreference to the accompanying drawings. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Oneskilled in the art may be able to use the various embodiments of theinvention.

FIG. 1 illustrates a typical loop recorder data-capture sequence overmultiple trigger events. Sensors monitor data 101 and detect events ofinterest 102. Upon detection of an event 102, a corresponding eventtrigger, such as a data-capture trigger pulse 103, is generated toprompt the data loop recorder to capture the incoming data 101 during acapture window 104. The data recorded in the memory is latertransferred, downloaded or read by an operator for analysis. Data 101may be from any source and may comprise any information, such asphysiological, environmental, meteorological, or seismic data, withoutlimitation. It is not possible to predict when events 102 will occur orwhen data-capture trigger pulse 103 will be send to the data looprecorder. Trigger pulses 103 may occur sporadically at intervals thatare longer than the desired data-capture window 104. For example,individual events 102 and triggers pulses 103 may occur every fewseconds or longer, but the data of interest may last only a fewmicroseconds or milliseconds. Thus, the data-capture duty-cycle may besmall in some embodiments.

Data that arrives before a specific event 102 or trigger pulse 103 (i.e.pre-event data) may be of interest and should be captured by the dataloop recorder. However, because the occurrence of the events 102 is notknown ahead of time, the data loop recorder must always be powered-on tocapture pre-event data. Given the low data-capture duty-cycle, the powerconsumption required to capture pre-event data in known data looprecorders is excessive.

If the monitoring device and data loop recorder memory have unlimitedaccess to power, then the memory can record in a continuous loop. Insuch a case, data-capture window can be configured to capture pre-eventdata that occurs before trigger pulse 103, but that has already beencaptured by the continuous loop memory. However, if the data looprecorder memory runs off of a limited power supply, such as a battery,then such continuous recording would rapidly drain the power supply. Itmay not be feasible to recharge the power supply or replace batteries ifthe data loop recorder is deployed in an inaccessible device, such as adown-hole drilling sensor, remote terrestrial seismic monitor,physiological sensor, or space-based meteorological or environmentalmonitor. Embodiments of the present invention provide for reduced powerconsumption in data loop recorders thereby allowing them to capture dataover a longer period on limited power.

FIG. 2 is a block diagram of a data loop recorder 200 according to oneembodiment of the invention. Inner Loop Memory (ILM) 201 is divided intoa plurality of segments 202. Outer Loop Memory (OLM) 203 is divided intoa plurality of segments 204. Auto Address Logic (AAL) 205 controls datastorage and addressing in ILM 201 and OLM 203. Energy Management System(EMS) 206 controls the power for OLM 203 and memory segments 204.Incoming data is received over data bus 207 and written to ILM 201 andOLM 203 at segments and addresses designated by AAL 205 upon detectionof an event trigger 208.

ILM 201 records all incoming data into an active segment. For example,before a first event is detected, ILM segment 1 (202 a) acts as acircular buffer and stores all incoming data. AAL 205 controls howincoming data is written into ILM segment 1 (202 a). When ILM segment 1(202 a) is full, AAL 205 overwrites older data in the same segment bymoving to the top of the segment and storing the additional incomingdata. AAL 205 continues to overwrite the data in ILM segment 1 (202 a),looping back to the top of the segment every time the segment fills up.The data stored in ILM 201 is the pre-event data. The size of segments202 is selected based upon the desired amount of pre-event data. In oneembodiment, for example, segments 202 are sized to record 1 second ofpre-event data. Accordingly, after every second, new incoming data 207overwrites the existing data in an ILM segment 202.

In one embodiment, ILM 201 is always powered-on. In other embodiments,portions of ILM 201 can be powered-off depending upon the system'slow-power requirements. For example, EMS 206 may control the power tosegments of ILM 201. EMS 206 may power-off segments of ILM 201 that arenot required to capture a pre-event data for a current event. Theunneeded segments of ILM 201 are placed in stasis mode, while othersegments of ILM 201 are powered-on to capture pre-event data.

When an event is detected and an event trigger 208 is received, EMS 206powers-on OLM 203 and AAL 205 begins storing post-event data to thecorresponding segment 1 (204 a) of OLM 203. In one embodiment, eachevent is recorded in a separate pair of segments 202/204. The number ofsegments 202 and 204 is selected based upon the maximum number of eventsto be recorded. The size of segments 204 is selected based upon thedesired amount of post-event data to be recorded. In one embodiment, forexample, segments 204 are sized to record 15 seconds of post-event data.It will be understood that the size of segments 202/204 and the amountof data to be recorded in each segment depends upon the correspondingmonitoring application and the type of data to be recorded. The range ofdata to be stored in typical applications may range from milliseconds tominutes, but may be a longer or shorter time.

In one embodiment, the pre-event data for a first event remains in ILMsegment 1 (202 a) and post-event data for the first event is stored inOLM segment 1 (204 a). When the event data is read out, AAL 205 controlsthe memory access and seamlessly reads the data out of the appropriatesegments so that data loop recorder 200 appears as a single memorydevice. AAL 205 maintains pointers to the starting point of thepre-event data in each segment 202—i.e. a pointer to the oldest data inthe segment. Because data is stored to ILM segments 202 in a circularmanner, the starting point for the data is continually changing andcould occur at any point in the segment, not just at the beginning ofthe segment.

In another embodiment, pre-event data from ILM segment 202 is moved tothe corresponding OLM segment 204 so that all of the data for each eventis stored in OLM 203 and can be read out directly from OLM 203 by AAL205. Space can be reserved at the beginning of each OLM segment 204 forthe pre-event data. The pre-event data may be moved to the OLM segment204 upon receipt of an event trigger, or during or after the recordingof the post-event data.

In an alternative embodiment, post-event data may be written directly toILM 201. After capturing the data during the designated post-eventperiod, the data may be transferred from ILM 201 to OLM 203 for storage.

At least some segments of ILM 201 is always powered-on to capturepre-event data, while other segments of ILM 201 and OLM 203 areselectively powered-on to capture post-event data. EMS 206 providesdynamic power management for ILM 201 and OLM 203. EMS 206 may power-onthe entire OLM to record post-event data or may power-on selectedsegments only. After event data has been stored, EMS 206 puts OLM 203 ina stasis mode that provides only enough power required to maintain thestored data. It will be understood by those of ordinary skill in the artthat EMS 206 may control the power consumed by OLM 203 in a number ofdifferent ways. For example, EMS 206 may use power gating to control thepower supplied to individual segments of OLM 203 or to OLM 203 as awhole. Alternatively, EMS 206 may use clock gating to limit the usage ofOLM 203 and, therefore, limit the power consumed by OLM 203. Bycontrolling the number of transactions sent to OLM 203, EMS 206 canlimit the power consumed by the memory.

The specific types of memory selected for ILM 201 and OLM 203 should beoptimized for their respective uses. ILM 201 and OLM 203 do not have tobe of the same type, but can be independently selected based uponleakage current and dynamic power requirements. ILM 201, which isrunning all the time, is preferably optimized for low dynamic power orlow access current. ILM 201 may be a ping-pong or dual buffering memory.For example, ILM 201 may be a small, low-power SRAM with an access powerof approximately 50 pJ and a standby current of approximately 100 nA.OLM 203, which is usually in a standby or stasis mode, is preferablyoptimized for low leakage current. For example, OLM 203 may be FRAM orFlash memory with an access power of approximately 200 pJ and a standbycurrent of approximately 50 nA. OLM 203 may comprise non-volatile memoryin which selected memory blocks are powered up by EMS 206 only duringwrite time and then powered-off after event data is captured.

FIG. 3 illustrates a loop recorder data-capture sequence according toone embodiment of the invention. Data 301 is monitored and continuouslyrecorded into a segment of an ILM, where data is overwritten by new datauntil an event is detected. The amount of current data stored in the ILMcorresponds to the size of pre-trigger data-capture window 304. When anevent of interest 302 is detected, the monitoring device sendsdata-capture trigger pulse 303 to the data loop memory. Trigger pulse303 causes OLM stasis-mode signal to shift from high (stasis-mode on) tolow (stasis-mode off), which in turn activates the OLM. Data is thenstored to the OLM for the duration of post-trigger data-capture window305.

FIG. 4 is a block diagram illustrating the capture and storage of datafor multiple events according to one embodiment of the invention. Data401, such as environmental or seismic information detected by a remotesensor, is captured by ILM 402, which loops (41) within first ILMsegment 403 storing data in real-time. When Event A is detected, OLM 404is powered-on and post-event data 401 is routed to first OLM segment405. OLM 404 typically requires some finite power-up time from detectionof an event until OLM 404 is fully powered-on and ready to record eventdata. During this power-up time, ILM 402 captures the post-event datauntil OLM 404 is fully powered-on and begins to capture post-event data.During post-event data capture or at the end of the designateddata-capture window, the data from ILM segment 403 may be transferred toOLM 404 for storage. This allows all of the Event A data to be stored inOLM segment 405 to maximize energy savings. After the data has beenstored to OLM segment 405, the OLM 404 is powered-off. In an alternativeembodiment, the data associated with Event A may be divided between ILMsegment 403 and OLM segment 405.

An AAL (not shown) keeps track of the events and maintains pointers tomemory locations in ILM where the events begin. As incoming data isreceived, the AAL uses a pointer to track the current location of thedata looping within an ILM segment. Upon detection of an event, the AALstores the current location 406 of the pointer. This locationcorresponds to the start of the pre-event data within the segment. TheAAL also stores a pointer to the corresponding OLM segment 405 thatcaptures the post-event data. When the pre-Event A data has beentransferred from ILM 403 to OLM segment 405, the AAL updates thepointers for the pre- and post-Event A data to point to locations insegment 405.

After capturing the Event A data, new incoming data 401 is stored tosecond ILM segment 407. Again, data is overwritten (42) within segment407 until Event B is detected. At that time, OLM 404 is again powered-onand data 401 is routed to second OLM segment 408, which capturespost-event data for Event B. During post-event data capture, or at theend of the designated data-capture window, the Event B data istransferred from ILM segment 407 to OLM segment 408 so that all of theEvent B data will be stored in one location. The OLM 404 is thenpowered-off. In an alternative embodiment, the Event B may be dividedbetween ILM segment 407 and OLM segment 408. The AAL stores the locationof pointer 409, which corresponds to the start of the pre-event data forEvent B. The AAL also stores a pointer to OLM segment 408, which holdsthe post-event data for Event B. When the pre-event data is moved fromILM segment 407 to OLM segment 408, the pointers are updated to reflectthe stored locations of the Event B data.

The capture of data as illustrated in FIG. 4 is useful for situations inwhich events occur at relatively widely spaced intervals that are longerthan the designated data-capture window. If Event B instead occurredduring the data-capture window for Event A in FIG. 4, then the pre-eventdata (and some of the post-event data) for Event B would overlap thedata for Event A and would be stored in segment 405. In such a case, theAAL would have to maintain a pointer to segment 405 to identify thestart of the Event B data.

FIG. 5 is a block diagram illustrating the capture and storage of datafor multiple events according to another embodiment of the invention.Incoming data 501 is captured by ILM 502, which loops (51) within firstILM segment 503 storing data in real-time. When Event A is detected, theincoming post-event data 501 is stored to second ILM segment 504 withoutlooping or overwriting. The AAL maintains a pointer to location 506within segment 503 to mark the start of the pre-event data. At the endof the designated data-capture window, OLM 504 is powered-on and thedata for Event A is transferred from ILM 502 to first OLM segment 505.Using the pointer 506, the data for Event A can be transferred to OLM504 and stored in chronological order. When the data has been stored tosegment 505, the OLM 504 is powered-off and placed in stasis-mode.

FIG. 5 also illustrates a second event, Event B that occurs within thedata-capture window for Event A. As a result of the proximity of EventsA and B, the data for their respective data-capture windows overlaps.The AAL maintains a pointer 507 to identify the beginning of the Event Bdata. In this case, at the end of the Event A data-capture window, ILM502 continues to record incoming data 501 for the duration of the EventB data-capture window. After capturing the Event B data, OLM 504 can bepowered-on and the Event B data transferred to second OLM segment 508.The pre-event data for Event B overlaps with the Event A data andincludes, for example, post-Event A data portion 52 and pre-Event A dataportion 53. The AAL identifies the pre-Event B data by moving back theappropriate duration from the Event B pointer 507.

In one embodiment, the transfer of the Event A data to OLM 505 may bedelayed until the Event B data has been captured. Alternatively,depending upon the DMA and memory speed and the rate of incoming data501, the Event A data may transferred during the Event B data-capturewindow.

If additional events occur during the data-capture window for Event A orB, then ILM 502 continues to store incoming data 501 for subsequentdata-capture window periods until data for each event has been capturedand transferred to OLM 504. After the data for Event B (or the lastevent) has been captured by ILM 502, additional data is stored in thenext available ILM segment 509 while the earlier event data istransferred to OLM 504.

FIG. 6 is a block diagram of a monitoring device 600 comprising oneembodiment of the data loop recorder disclosed herein. Monitor 600 iscoupled to a sensor 601 via input interface 602. Sensor 601 may beintegral to or physically separate from monitor 600. An incoming datastream is received from sensor 601 at input 602 and passed to ILM 603and OLM 604 over data bus 605. DMA 609 controls the transfer of databetween ILM 603 and OLM 604. Processor 606 controls the operation ofmonitor 600 and the data loop recorder. In the embodiment illustrated inFIG. 6, AAL 607 and EMS 608 are state machines running on processor 606.In other embodiments, the AAL and/or EMS may be embodied as a softwareor firmware running on processor 606 or a separate device, such as aspecialized chip or Application Specific Integrated Circuit (ASIC).Processor 600 monitors incoming data from sensor 601 and identifiesdesignated events. Upon detection of a designated event, processor 600sends an event trigger to AAL 607 and EMS 608 to prompt recording ofpre-event and post-event data in ILM 603 and OLM 604.

AAL 607 maintains pointers to memory locations in ILM and OLMcorresponding to where captured data begins for each event. The pointersallow the AAL to make sense of the recorded data and to manage thecorrect reading out of the data. AAL 607 may maintain a table ofpointers or registers that identify the location of each event. Thetable may comprise, for example, an event identifier, a timestamp, apointer to the event data in the ILM, pointer to the event data in theOLM, and a description of the event that caused the data capture. AAL607 controls the transfer of data into and out of ILM 603 and OLM 604.Data may be downloaded from monitor 600 via output interface 610 forreal-time or offline processing as required by the monitored events andmonitoring application. Data may be downloaded or output to a personalcomputer 611, for example. Data may be transferred out of monitor 600 inany known manner, such as by direct connection, wireline transfer orwireless transmission.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions,and the associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A recording device, comprising: a first memory partitioned into aplurality of first segments; a second memory partitioned into aplurality of second segments; an address logic circuit coupled to thefirst memory and to the second memory, the address logic circuitcontrolling read and write locations for data stored to the first memoryand to the second memory; and an energy management system coupled to thesecond memory, the energy management system controlling a power state ofthe second memory.
 2. The recording device of claim 1, furthercomprising: the energy management system coupled to the first memory,the energy management system controlling a power state of segments ofthe first memory.
 3. The recording device of claim 1, furthercomprising: a data bus coupled to the first memory and the secondmemory; and wherein a selected segment of the first memory acts as acircular buffer and real-time data received on the data bus is stored tothe selected segment.
 4. The recording device of claim 3, furthercomprising: a processor coupled to the address logic circuit, the energymanagement system, and the data bus, the processor monitoring datareceived on the data bus and identifying designated events.
 5. Therecording device of claim 4, wherein the processor sends an eventtrigger to the address logic circuit and to the energy management systemupon detection of a designated event.
 6. The recording device of claim1, wherein the address logic circuit further comprises a pointer tableidentifying locations of stored data for a plurality of events.
 7. Therecording device of claim 1, wherein the energy management systemsupplies power to the second memory upon detection of an event trigger,and wherein the address logic circuit causes data to be stored to thesecond memory upon detection of the event trigger.
 8. A method forstoring data, comprising: storing first pre-event data to a firstsegment of a first memory, the first segment operating as a circularbuffer to store a selected duration of recent data; receiving a firstevent trigger; storing first post-event data received after the firstevent trigger beginning at a second segment of the first memory during afirst data-capture period; powering-on a second memory; and transferringthe first pre-event data and first post-event data to a first segment ofthe second memory.
 9. The method of claim 8, further comprising: storinga pointer to a location in the first memory corresponding to receipt ofthe first event trigger.
 10. The method of claim 8, wherein the secondmemory is powered-on at the end of the first data-capture period. 11.The method of claim 8, wherein the first pre-event data and firstpost-event data is transferred to the first segment of the second memoryat the end of the first data-capture period.
 12. The method of claim 8,wherein powering-on the second memory comprises: powering-on onlyselected segments of the second memory.
 13. The method of claim 8,wherein powering-on the second memory comprises: powering-on allsegments of the second memory.
 14. The method of claim 8, furthercomprising: receiving a second event trigger during the firstdata-capture period; storing second post-event data to the first memoryduring a second data-capture period, wherein the second data-captureperiod overlaps the first data-capture period; identifying secondpre-event data within data stored for the first event; and transferringthe second pre-event data and second post-event data to a second segmentof the second memory.
 15. The method of claim 14, further comprising:storing a pointer to a location in the first memory corresponding toreceipt of the second event trigger.
 16. A method for storing data,comprising: storing pre-event data to a first segment of a first memory,the first segment operating as a circular buffer to store a selectedduration of data; receiving an event trigger; powering-on a secondmemory; storing post-event data received after the event trigger to afirst segment of the second memory during a data-capture period; and atthe end of the data-capture period, powering-off the second memory. 17.The method of claim 16, further comprising: transferring the pre-eventdata to the first segment of the second memory.
 18. The method of claim17, wherein the pre-event data and post-event data are combined inchronological order in the first segment of the second memory.
 19. Themethod of claim 16, further comprising: storing a pointer to a locationin the first memory corresponding to receipt of the event trigger. 20.The method of claim 16, further comprising: storing second pre-eventdata to a second segment of the first memory, the second segmentoperating as a circular buffer to store the selected duration of data;receiving a second event trigger; powering-on the second memory; storingsecond post-event data received after the second event trigger to asecond segment of the second memory during a second data-capture period;and at the end of the second data-capture period, powering-off thesecond memory.
 21. The method of claim 20, further comprising: storing apointer to a location in the first memory corresponding to receipt ofthe second event trigger.
 22. A recording device, comprising: a firstmemory partitioned into a plurality of first segments, sizes of thefirst segments selected to provide storage for a predetermined pre-eventtime period, the first memory optimized relative to a second memory torequire low access power; the second memory partitioned into a pluralityof second segments, sizes of the second segments selected to providestorage for a predetermined event period, the event period comprisingthe pre-event period and a post-event period, the second memoryoptimized relative to the first memory to require low static power; andan address logic circuit coupled to the first memory and to the secondmemory, the address logic circuit controlling read and write locationsfor data stored to the first memory and to the second memory.
 23. Therecording device of claim 22, further comprising: an energy managementsystem coupled to the second memory, the energy management systemcontrolling a power state of the second memory.
 24. The recording deviceof claim 23, further comprising: the energy management system coupled tothe first memory, the energy management system controlling a power stateof segments of the first memory.
 25. The recording device of claim 22,wherein the segments of the first memory act as circular buffers forstoring real-time data.
 26. The recording device of claim 22, whereinthe address logic circuit further comprises a pointer table identifyinglocations of data stored for a plurality of events.
 27. The recordingdevice of claim 22, wherein the energy management system supplies powerto the second memory upon detection of an event trigger, and wherein theaddress logic circuit causes data to be stored to the second memory upondetection of the event trigger.